(6 of )Darin Garcia looks at the remains of his home he's lived in for nearly 40 years as he embraces Ashley Alva s, Monday Oct. 9, 2017 in the Coffey Park area of Santa Rosa. (Kent Porter / Press Democrat) 2017

(7 of )Smoke from regional wildfires obscures the skyline in San Francisco, Thursday, Oct. 12, 2017. Gusting winds and dry air forecast for Thursday could drive the next wave of devastating wildfires that are already well on their way to becoming the deadliest and most destructive in California history. (AP Photo/Jeff Chiu)

Smoke, fire leads to dirtiest air ever recorded in Sonoma County as high winds expected to return

Sonoma County remained cloaked in the dirtiest air ever recorded in the region for the third straight day Wednesday, the result of smoke-belching fires that threatened to expand as dangerously strong winds return to the area.

The National Weather Service warned the region will be raked Thursday by high winds, with gusts up to 50 mph, recreating some of the treacherous conditions that spawned the fast-moving fires late Sunday night.

Winds were not expected to be quite as strong as the 60 mph blasts that propelled the Tubbs fire over the mountains from Napa County into Santa Rosa early Monday, said Brian Garcia, a weather service meteorologist.

Nonetheless, firefighters are worried the windy conditions could hamper efforts to douse the fires burning in the region, particularly winds from the north that could push fires toward populated areas.

“The concern is it’s going to be a little bit too much for all of us to deal with and the fire will grow,” Santa Rosa Fire Chief Tony Gossner said Wednesday. “It won’t grow as fast as it did Sunday but we think all the fires are going to get a little bigger tonight.”

Thursday’s wind warning called for northeast winds in the mountains from 20 to 30 mph with gusts over 50 mph through 5 p.m. It applied to the mountains between Napa and Sonoma counties and the hills flanking Sonoma Valley, as well as the mountains in eastern Napa County. The warning also applied to the mountains in northwest Sonoma County.

In Sonoma County valleys, including Santa Rosa, winds are expected to be calm overnight, picking up toward sunrise Thursday, Garcia said.

Smoke from the North Bay wildfires, meanwhile, is fouling the air throughout the San Francisco Bay Area, the regional air monitoring agency said.

“Very unhealthy air quality from the wildfires in the North Bay is causing unprecedented levels of air pollution throughout the Bay Area. Due to active wildfires and changing wind patterns, air quality could be impacted for many days to come,” the Bay Area Air Quality Management District warned.

The district urged residents impacted by heavy smoke to seek shelter in buildings with filtered air or move to areas outside the region until smoke levels subside. Children, the elderly and people with respiratory conditions are most vulnerable.

“We’ve not seen levels of pollution this high for this long before,” said Kristine Roselius, air district spokeswoman. Air quality monitoring dates back to the 1980s, she said.

Napa, Vallejo and Concord had air deemed “very unhealthy” Wednesday, the district reported. Oakland, Berkeley, San Pablo, Livermore, Redwood City and San Jose had “unhealthy” air.

In the North Bay, San Rafael and Sebastopol had air deemed “unhealthy for sensitive groups,” the next milder rating. All three ratings indicate small particle pollution exceeding the federal health standard.

In many areas of Lake County, air has reached the unhealthy range since Monday and may or may not improve by Thursday, depending on wind and fire activity, said Douglas Gearhart, the county’s air pollution control officer.

Staff Writer Randi Rossman contributed to this report. You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.